Total CO 2, 13C, and dissolved oxygen - 18O at Geosecs II in the North Atlantic

Abstract

This paper presents profiles of ΣCO 2, δ 13C in ΣCO 2, dissolved O 2, and δ 18O in dissolved O 2, measured at Geosecs II in the North Atlantic. The O 2 minimum at 1000 m is accompanied by a minimum in δ 13C and a sharp maximum in δ 18O; ΣCO 2 increases downward through this layer with a slope change. All four parameters are remarkably uniform in the deep and bottom water below the O 2 minimum, almost to the precision of measurement. Relative to data previously reported from this area of the Atlantic, our ΣCO 2 values are 3% lower than those of Li et al. [10], and our δ 13C values are up to 2‰ greater than those of Deuser and Hunt [12]. Also, our δ 18O enrichments in dissolved O 2 are very much less than Pacific values reported by Dole and coworkers [15]. All of these differences are attributed principally to bacterial O 2 consumption during sample storage by previous workers, due to lack of, or inadequate, poisoning. In contrast to the North Atlantic, there is a very large gradient of dissolved O 2 in the vertical profile of North Pacific Deep Water; however, if the mean deep-water O 2 concentration is compared with the uniform value in North Atlantic Deep Water, the O 2 and ΣCO 2 differences in North Atlantic and North Pacific Deep Water are essentially equimolar at 160 μm/kg. If 77% of deep-water O 2 consumption is used for oxidation of organic carbon (the R-K-R “model plankton” value), the increase in ΣCO 2 in Pacific deep water is about 25% due to dissolution of carbonate, and 75% due to oxidation of organic matter, in the vertical particulate flux. These proportions are in agreement with those estimated from alkalinity-ΣCO 2 variations [10]. Our δ 13C measurements in the Atlantic are quite consistent with the ΣCO 2-O 2-alkalinity variations between the Atlantic and Pacific deep water; thus the disagreement previously noted [14] is attributed to storage effects on δ 13C measurements by previous workers, as noted above.